Pressure sensors have become ubiquitous the past few years as they have found their way into several new types of products. Utilized in automotive, industrial, consumer, and medical products, the demand for pressure sensors has skyrocketed and shows no signs of abating.
Pressure sensors typically include a diaphragm or membrane. When a pressure sensor experiences a pressure, the membrane responds by changing shape. This change in shape causes one or more characteristics of electronic components on the membrane to change. These changing characteristics can be measured, and from this the pressure can be determined.
Often, the electronic components are resistors that are configured as a Wheatstone bridge located on the membrane. As the membrane distorts due to a pressure, the resistance of the resistors change. This change results in an output of the Wheatstone bridge. This change can be measured using wires or leads attached to the resistors.
These pressure sensors may be used to measure the pressures of fluids and gasses that are fairly benign. For example, these pressure sensors may be used to measure air pressure in a tire or similar environment. In such situations, the resistors and leads may be placed in the fluid to be measured without, or with only minimal, protection.
However, often these pressure sensors may be used in a more harsh or corrosive environment. For example, pressure sensors may be used to measure pressures of blood, gasoline, and other harsh or corrosive substances.
Exposure to such environments may corrode or degrade the leads and resistors of the pressure sensors. This exposure may lead to inaccurate or inconsistent pressure readings, and it may eventually lead to a failure of the device.
Additionally, forming electrical connections in close proximity to the sensitive membrane could produce a change in shape in the membrane, leading to a change in the output that is both undesirable and unpredictable.
Moreover, as device dimensions continue to shrink, it may become increasingly difficult to create electrical connections in close proximity to the sensitive membrane without incurring any damage to the membrane.
Thus, what are needed are circuits, methods, and apparatus that provide pressure sensors that may be used in harsh or corrosive environments, reduce damage to the membrane due to forming electrical connections and reduce permanent stress on the membrane caused by connections made in close proximity to the membranes.